Line two 4x8-inch loaf pans with foil; coat with cooking spray. Stir together berry blue gelatin and 1/4 cup sugar in a bowl with 1 1/2 cups boiling water until dissolved. Pour into the first prepared pan. Stir together strawberry gelatin and remaining 1/4 cup sugar in a bowl with 1 1/2 cups boiling water until dissolved. Pour into second prepared pan. Chill both mixtures until set, at least 3 hours.,______,Meanwhile, line a 9x13-inch pan with foil, leaving a 2-inch overhang on long sides, and coat with cooking spray. Turn chilled gelatins out onto a cutting board and coarsely chop. Transfer to prepared pan, then pour in milk mixture. Chill until set, at least 3 hours.,Use foil to carefully lift gelatin mixture and transfer to a baking sheet, then fold down edges of foil. Insert 8 wooden sticks, spaced evenly, on each long side of the gelatin block. Freeze overnight.,Let frozen gelatin stand at room temperature 15 minutes. Cut into 16 ice pop-sized rectangles.